1. File Systems

2. Secondary storage management
Disk space management
Free space management
Disk is divided into blocks or sectors.

3. Disk space management When to allocate space? Portion size
Pre-allocation vs. dynamic allocation.
Portion size
Large variable-sized portions consisting of contiguous blocks
Placement algorithms – Best fit, First fit and Next fit
Small fixed portions (non-contiguous blocks)

4. Disk space management File allocation methods
Keep track of which sectors/blocks on the disk belong to which logical file/directory.

5. Contiguous File Allocation
What happens if file F requires 6 blocks?

6. Contiguous allocation

7. File allocation method - Chained allocation/Linked list

8. Chained allocation/Linked list

9. Chained allocation after consolidation

10. Linked list allocation with an index
File A occupies a total of _______ blocks and they are ________________.
File B occupies a total of _____ blocks and they are __________________.

11. Linked list allocation with index
A table is maintained in memory which acts as the linked list.
Don’t have to access the disk to get the next pointer
More efficient with random access files.
Used in MS-DOS

12. Indexed allocation

13. Free space management Disk allocation table
to keep track of all the used and unused blocks on the disk.